Method of making a Raney copper catalyst and the catalyst so made

ABSTRACT

An improved process for making a Raney copper catalyst which contains from about 2 to 45 weight percent of aluminum on a 100 weight percent total weight basis. Preferably, this catalyst is prepared under low temperature, and/or slow caustic addition conditions from a copper aluminum alloy.

RELATED APPLICATION

This application is a continuation-in-part of our earlier filed U.S.patent application Ser. No. 458,435 filed Apr. 5, 1974, now U.S. Pat.No. 3,920,740, which is a continuation-in-part of U.S. Pat. applicationSer. No. 408,238 filed Oct. 19, 1973, now abandoned, which is acontinuation-in-part of U.S. Pat. application Ser. No. 280,686, filedAug. 14, 1972, now abandoned.

BACKGROUND OF THE INVENTION

In the art of catalytically hydrolyzing acrylonitrile with water toacrylamide, various copper and copper containing catalysts have beenproposed, such as mixtures of copper oxide with other metal oxides,reduced copper oxide/metal oxide mixtures, copper and copper/metalmixtures (see U.S. Pat. Nos. 3,597,481; 3,631,104; 3,642,894; and3,642,643). The use of Raney copper catalysts for this purpose is shownin Ger. Pat. No. 2,036,126, German DOS 2,164,185 (1972), Canadian Pat.839,384 (1972) and apparently also in Asahi et al Japanese Publication69/5205 (published April 3, 1969; filed May 13, 1966 as Jap. ApplicationNo. 66/29,948). Based upon the method of catalyst preparation, it wouldappear that such prior art can be cataloged into two groups, one groupinvolving the reduction of a copper containing compound or compounds,the other group involving the activation of a copper or copper alloy(such as Raney copper). See also U.S. Pat. No. 3,767,706.

So far as can be determined, when using a Raney copper catalyst tohydrolyze acrylonitrile to acrylamide by the teachings of the prior art,it has been the practice to prepare such catalyst in the manner ofKawaken Fine Chemicals Co., Ltd. of Tokyo, Japan (see, for example, theabove referenced Canadain Pat. No. 839,384 at p. 5 where it is indicatedthat the Raney copper catalyst there used was obtained from Kawaken FineChemicals Co.,). Kawaken Fine Chemicals Co. report in their tradeliterature that the starting alloy (for example a 50:50 weight ratiomixture copper and aluminum) is crushed, screened to size, and immersedinto aqueous alkali to dissolve out virtually all of the aluminum, afterwhich the resulting activated product is kept under water or inertsolvents to avoid oxidation. Apparently complete aluminum removal washeretofore believed to be desirable for purposes of enhancing catalystactivity for this intended hydrolysis reaction.

A recent study of the immersion of such alloy particles into aqueousalkali suggests adverse effects upon catalyst activity are caused byoverheating of alloy particles during activation with caustic. Forexample, when about 20 to 30 wt. % sodium hydroxide dissolved in wateris contacted with starting alloy particles at the ratio of about 100 to120 weight percent total caustic per 100 parts starting alloy particleswith the alkali solution being maintained at a fixed temperature in therange from about 140 to 248° F and with particle immersion time in suchsolution of 2 to 3 hours, heat is generated in a relatively shortinitial period in the immersion during which the aluminum is rapidlyreacted away from the starting alloy. Presumably, the individualparticles experience on their surfaces strong localized heating duringthis period. Such a thermal history, for reasons not altogether clear,is apparently responsible for a reduction in the catalytic activity ofthe product caustic-activated Raney copper catalyst in the catalytichydrolysis in water of acrylonitrile to acrylamide. Such productcatalyst produced by such immersion contains not more than about 0.5weight percent aluminum on a 100 weight percent basis and this catalystis typically in the form of a finely divided solid material.

Apparently, prior art Raney copper catalysts are prepared by changingstarting alloy particles to a caustic solution. These particles areusually small in size to enhance and accelerate aluminum dissolutionfrom the starting alloy and achieve thereby a maximum removal ofaluminum initially present in such starting particles. This smallparticle, caustic activated product catalyst may be better suited foruse as a suspension catalyst (see Mitsui Toatsu Chemicals, Ger. DOS2,240,783) than as a fixed bed catalyst in such hydrolysis reaction. Thecharacteristically low activity of catalysts produced in this mannerjust described dictates the use of a high surface area catalyst system,i.e. a system of very small catalyst particles, to enhance thehydrolysis rate of acrylonitrile to acrylamide (independently ofreactant relative concentrations). These prior art catalyst particleshave typically a limited or relatively low initial catalyst activity,and also have a relatively short half life. They are shown in the priorart on acrylonitrile hydrolysis to acrylamide to operate on dilute,starting aqueous acrylonitrile feeds.

Recent studies of Raney copper catalysts used in the art of hydrolyzingacrylonitrile to acrylamide show that the conditions of activation exerta profound influence upon the properties of the product catalyst innitrile hydrolysis. Because of the limitations and shortcoming aboveindicated for prior art Raney copper catalysts, the art continues toseek a Raney copper catalyst adapted for such hydrolysis reaction whichhas a high initial activity and a long activity half life, and which,additionally, is particularly well suited for hydrolyzing acrylonitrilein a concentrated acrylonitrile/water feed at a rapid rate and at a highconversion level. Preferably, it would be beneficial to the art to havea Raney copper catalyst with such properties which, in addition, couldreadily be and conveniently prepared in particle sizes large enough topermit use of the activated product a fixed catalyst bed, as opposed toa suspension or fluidized bed system, for example.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an improved Raney copper catalystand to a method for making the same. This catalyst comprises from about2 to 45 weight percent aluminum with the balance up to 100 weightpercent being copper. More preferably, such catalyst comprises, on a 100weight percent total weight basis, from about 9 to 40 weight percentaluminum with the balance up to 100 weight percent thereof being copper.This catalyst has an average particle size in the range from about 0.002to 0.5 inch. This catalyst is prepared by a particular process as taughtherein.

Because of the characteristically high initial catalytic activity andthe characteristically long life associated with such a catalyst whenused in a process wherein acrylonitrile is hydrolyzed with water toacrylamide, the present invention provides a catalyst which isparticularly useful in such a catalytic hydrolysis process which can beoperated continuously and for extended periods of time with the samecatalyst to produce desired, economically significant, high conversionyields of acrylamide from acrylonitrile at economically significant highrates of conversion. The invention is particularly useful, and theforegoing advantages are particularly well demonstrated, when usingstarting compositions containing a high, or concentrated acrylonitrilecontent. In such a catalytic conversion process typically, such astarting composition comprises from about 10 to 75 weight percentthereof being comprised of water. Preferably, such composition containsabout 30 to 40 weight percent acrylonitrile (same basis). At theseconcentrations, the acrylonitrile and water are not completely miscible.The process is conducted under liquid phase conditions usingtemperatures in the range from about 150 ° to 300° F., with temperaturesof from about 160° to 250° F. being presently preferred.

The present invention provides an improved technique for activating aRaney copper catalyst which is adapted for use in a process forhydrolyzing acrylonitrile to acrylamide under aqueous liquid phaseconditions.

Further, the present invention aims to provide a Raney copper catalystwhich permits one to hydrolyze acrylonitrile to acrylamide substantiallyfree of by-product formation and achieve a higher initial activitytogether with a longer catalyst life than has heretofore been possible.

Other and further aims, objects, purposes, advantages, utilities andfeatures will be apparent to those skilled in the art from a reading ofthe present specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagrammatic representation of one mode of preparing acatalyst suitable for the process of the present invention;

FIGS. 2 through 4 each show representations similar to FIG. 1 butillustrating second, third, and fourth modes, respectively, the effecton reaction rate of temperature, particle size, and causticconcentration.

DETAILED DESCRIPTION

The catalyst provided by the present invention is a Raney copperforaminous catalyst which has been specially activated. The startingmaterial for this catalyst is a preformed binary Al/Cu alloy whichcontains a weight percent ratio of Al/Cu in the range from about 70:30to 30:70 (preferably about 45:55 to 55:45, and most preferably about50:50). The alloy particles further initially have average particlediameters in the range of from about 0.002 to 0.5 inch. This catalyst isfurther characterized by having a relative activity of at least about 2,and preferably in the range from about 2.5 to 3.5. For purposes of thepresent invention "relative activity" is measured as described inExample 5 hereinbelow.

This catalyst is, in general, preparable by contacting a group ofcooper-aluminum alloy particles with a liqud aqueous medium containingdissolved therein alkali metal hydroxide. The contacting is done whilemaintaining a reaction rate between said particles and said hydroxide insaid medium such that less than about 0.02 (preferably less than about0.01) moles of hydrogen per mole of said aluminum initially present insaid alloy on a 100 weight total initial alloy basis is evolved perminute. The contacting is conducted while keeping the bulk temperaturein said medium in the region of said group in the range from about 32°to 180° F about (0° to 82° C) and this contacting is continued until atleast about 25 weight percent of said aluminum initially present in saidalloy on a 100 weight percent total initial alloy basis is removed.

The total number of moles of alkali metal hydroxide charged to saidmedium during the total time of said contacting is at least about 0.5times the number of moles of aluminum initially present in said alloyparticles. The total weight of water initially in said medium at thebeginning of said contacting plus water added during said contactingranges from about 100 to 1.5 times the total weight of said alkali metalhydroxide charged to said medium.

Thus, in one mode, activation of this starting alloy is accomplished byprolonged addition (contacting) timewise of an aqueous solution ofalkali metal hydroxide (e.g. aqueous caustic) to a group of copperaluminum alloy particles. Such alkali metal hydroxide solution so addedcan contain from about 1 to 40 weight percent dissolved hydroxide,preferably, though solutions of alkali metal hydroxide having highercaustic contents (up to solution saturation) may be employed as startingleaching compositions for use in preparation (actuation) of the catalystused in the practice of the present invention. Alkali metal hydroxidemay also be added as solid pellets or flakes, although handling ofalkali metal hydroxide as a solution is generally preferred on acommercial scale for reasons of safety and economy. During suchaddition, the alkali metal hydroxide (leaching composition) reacts withand dissolves the aluminum in the starting alloy in amounts such thatthe amount of aluminum remaining in the so-leached solid catalystproduct ranges from about 2 to 45 weight percent (based on total leachedproduct weight), and preferably from about 9 to 40 weight percent (samebasis), but at least about 25 weight percent of the aluminum, andpreferably at least about 35 weight percent, thereof, initially presentin said alloy on a 100 weight percent total initial alloy basis isremoved.

In preparing the catalyst, the caustic solution and the resultingaqueous medium which contacts the copper/aluminum metal alloy havetemperatures in the range from about 32 to 180° F (and preferablytemperatures in the range from about 60 to 120° F). The group ofstarting alloy particles has a particle size diameter in the range fromabout 0.002 to 0.5 inch, as indicated, and the copper/aluminum alloy hasa starting copper to aluminum weight ratio of from about 30:70 to 70:30.

In this mode, the total time of contacting of caustic solution with suchparticles is typically and preferably accomplished over a total timeinterval of from about 2 to 30 hours, although longer times may beemployed even up to 200 hours, with the fresh or starting causticsolution preferably being added (contacted) gradually to such particlesover this time interval. The starting alloy particles may be initiallyimmersed in water before being contacted with caustic solution. Theresulting aqueous medium to which the starting hydroxide solution isadded can typically contain from about 0.5 to 40 weight percent (totalmedium basis) of dissolved alkali metal hydroxide; the starting alkalimetal hydroxide solution can contain from about 1 to 50% weight percent,more or less, of dissolved alkali metal hydroxide. In this mode, thecontact rate between a starting caustic (alkali metal hydroxide)solution and a group of copper/aluminum alloy particles ranges duringsuch contacting from about 0.01 to 7.0 moles of caustic (alkali metalhydroxide) per mole of aluminum initially present in the alloy particlesper hour.

As indicated, the alkali metal hydroxide is added incrementally to thereaction zone. It will be appreciated that the term "incrementally" asused herein is inclusive of both continuous alkali metal hydroxideaddition as well as discontinuous addition. Continuous alkali metalhydroxide is preferred for reasons of production simplicity. For presentpurposes, the contact rate is equivalent to the addition rate,generally.

The total quantity of alkali metal hydroxide so added to theparticle-contacting, alkali metal hydroxide medium ranges from about 0.5to 20 moles of alkali metal hydroxide per mole of aluminum initiallypresent in the alloy particles. After the alkali metal hydroxide hasbeen completely added to such medium, the contacting is preferablycontinued.

In this mode of catalyst activation by incremental caustic addition, onecan, for example, conveniently employ a total quantity of aqueous alkalimetal hydroxide such that the total molar quantity of hydroxide usedtotals from about 1 to 5 times the total molar amount of aluminum it isdesired to leach away, as when a batch preparation procedure is beingemployed where the aqueous hydroxide is being added to a vesselcontaining a fixed quantity of starting alloy, and such aqueoushydroxide leaching composition is allowed to accumulate in this vesselduring the leaching operation. Alternatively, for example, one canemploy a batch preparation procedure where the aqueous hydroxide used iscontinuously removed from the region of the alloy being leached aftercontact therewith so that fresh aqueous hydroxide can be continuously orintermittently brought into contact with such alloy being leached; inthis procedure, one can employ a larger total excess quantity ofstarting leaching composition during the leaching operation.

During the contacting of starting alloy with such leaching composition,an aluminate (in solution or dispersion) and hydrogen gas are produced.Conveniently, the hydrogen gas is vented more or less at the rategenerated from the reaction zone, and most of the aluminate is removedin the water of the leaching composition. As indicated, hydrogenevolution can be conventionally metered and used to control aluminumremoval rate, if desired, but, in general, the contacting conditionsused in the one mode herein above described involving incrementalcaustic addition can be used to produce a catalyst for use in thisinvention without direct measurement of hydrogen evolution especiallyafter reaction variables are one chosen and established within theranges above indicated.

In another mode of catalyst activation to produce a catalyst having analuminum content and an activity as indicated above one can employtemperature control rather than contacting rate as a primary means ofcontrolling production of desired catalyst from starting alloy particleswith alkali metal hydroxide. When so using temperature control, thoseskilled in the art will appreciate that the alkali metal hydroxideaqueous medium initially contains at least about 1.0 weight percentdissolved alkali metal hydroxide (and preferably at least about 10.0weight percent dissolved alkali metal hydroxide). The medium ispreliminarily cooled to a temperature which is not above 100° F andwhich is preferably not above about 70° F before being contacted withthe group of alloy particles. Optionally substantially all of saidalkali metal hydroxide can be initially present in such medium, and suchmedium is initially bulk added to a reaction zone wherein the alloyparticles are contained, and the bulk temperature is maintained belowabout 70° F during said contacting until at least about 25 weightpercent, and preferably at least about 35 weight percent, (total initialalloy weight basis) of the aluminum is removed.

In catalyst activation using either incremental addition of caustic orlow temperature, contacting is best achieved by maintaining theparticles of alloy in a substantially fixed reaction zone. The particlesmay be in a substantially fixed spatial position, or, if they are smallenough, they may be suspended in the fixed reaction zone in the alkalineaqueous reaction medium by means of agitation, medium circulation, orthe like. Thus the alkaline medium can be continuously agitated, or whenthe particles are maintained in a relatively fixed spatial position, themedium can be circulated through and around such. It is preferred toavoid masses of particles to minimize deleterious heat exposure thereof.

As the base for use in the catalyst activation procedure, one can employany alkali metal hydroxide; however, for reasons of commercialavailability, it is preferred to employ the sodium and potassiumhydroxides industrially used and available generally commercially. It ispreferred to conduct the activation operation under inert, nonoxidizing,atmosphere conditions, such as under a blanket of nitrogen gas, or a gasof the helium family, or the like.

Preferably, a catalyst for use in this invention is prepared in acontact time interval with aqueous alkali metal hydroxide solution whichranges from about 4 to 20 hours, and, more preferably, which ranges fromabout 6 to 12 hours.

In catalyst activation by this invention, a group of alloy particles isconfined to a reaction zone, and such a caustic solution is added intosuch a reaction zone. The resulting solution produced in contacting isallowed to accumulate in such zone. The starting group of alloyparticles may be initially wet with water, or may be initiallysubstantially free from water, as desired. In one preferred mode, theparticles are initially immersed in water before contact with caustic.Catalyst activation is preferably conducted under conditions whichminimize the rate of heat release from the highly exothermic reactionbetween base and starting alloy. As indicated, one convenient procedureis to employ small, incremental charges of leaching solutions during thereaction. In some instances as indicated the amount of aluminum removedmay be monitored by measuring hydrogen evolved during the reaction. Inother instances, analysis of the aluminum in the base solution may beused as a measure of aluminum removal from the alloy.

After the alloy has thus been activated with base (alkali metalhydroxide solution), it is then washed with water, preferably deionizedor distilled, primarily to separate therefrom any remaining unreactedcaustic. Conveniently, the resulting solid catalyst particles remainingare washed with water to a neutral pH (e.g. a pH below about 8 andpreferably in the range of from about 7.0 to 7.5). The product catalystcan then be removed from the reaction or activation zone. Preferably thecatalyst is wet screened to separate fines. The product catalyst can bestored, conveniently under water as in drums. Keeping the catalyst underwater prevents oxidation thereof as by air, which occurs rapidly if thecatalyst is allowed to have air or oxygen exposure.

To use in this invention, this washed catalyst is contacted with anaqueous composition comprising acrylonitrile and water, as indicatedabove, using temperatures as indicated above. The hydration reactionproceeds even when the amount of the catalyst used in this invention isvery slight. For example, addition of such catalyst in an amount as lowas about 0.01 gram per mole of acrylonitrile is sufficient to make theacrylonitrile hydrolysis reaction proceed. The greater the amount ofcatalyst used, the faster the reaction proceeds, other variables beingconstant, in general, thus permitting an increase in the amount ofacrylamide produced. Consequently, the amount of catalyst employed permole of starting acrylonitrile initially employed can preferably rangefrom about 0.01 to 100 grams.

Acrylamide may be made from a mixture of acrylonitrile and wateremploying the catalyst of the present invention using a suspension bed,or a fixed bed, of catalyst or combinations thereof. Two or morereactors may be connected in series. The reaction liquid and thecatalyst particles, as when a suspension bed system is employed, may becounter-currently moved to effect and enhance reaction.

Such a hydrolysis process may be practiced under atmospheric pressuresor slightly above, the latter being preferred, but the process may bepracticed at desired superatmospheric and subatmospheric pressuresdepending upon equipment considerations. Inert gas atmospheres, such asprovided by nitrogen, steam, or the like may be optionally employed tomaximize the conversion of acrylonitrile to acrylamide at given processconditions. Batch processing may be used, but continuous is preferred.

When practicing such hydrolysis process using such as Raney coppercatalyst prepared as described herein and utilizing a suspension bedsystem, it is preferred to employ the Raney copper catalyst in the formof particles having average diameters in the range from about 0.002 to0.100 inch. Similarly, when such hydrolysis process is practiced usingthe Raney copper catalyst in the form of a fixed bed, it is convenientand preferred to use the Raney copper catalyst in the form of particleshaving average particle diameters in the range from about 0.02 to 0.05inch.

In another preferred catalyst preparation procedure, using the preferredroute above described, the alloy particles are confined to a reactionzone. The caustic solution is first contacted with the group ofparticles of the zone and the resulting aqueous medium is graduallyremoved from the zone.

In another, more preferred, catalyst preparation procedure, using thepreferred route above described, the resulting aqueous medium is soremoved at a volumetric rate which is about equal to the rate ofaddition of said caustic solution.

In such a preferred procedure, substantially 100 weight percent of thisso removed resulting aqueous medium can be recycled back into contactwith the group of particles being activated. During such a recycle, theso recycled aqueous medium is admixed with at least a portion of freshcaustic solution before or during recycle contact with such group ofparticles.

Alternatively, less than 100 weight percent of the so removed resultingaqueous medium can be recycled back into contact with the group ofparticles. The balance up to 100 weight percent thereof is removed fromthe reaction zone and can be discarded. Caustic is preferably graduallyadded at a rate approximately equal to the rate at which the caustic isconsumed through reaction with the aluminum in the alloy. The processmay preferably be practiced continuously at a rate which isapproximately equal to the rate of consumption.

When hydrolyzing acrylonitrile to acrylamide with the catalyst of thisinvention, it is preferred to prepare such a catalyst with relativelylarge particles and to use a fixed bed catalyst in the reaction zone orzones employed. The amount of aluminum left in the catalyst after anactivation, as described herein, can vary widely, but, in the case of anactive catalyst used for fixed bed catalysis, it has been found that asmuch as about 10 to 15 weight percent aluminum (based on total catalystweight) can be present in a catalyst without apparently affectingcatalyst use and performance characteristics, such as conversion rate,throughput rate of reactants, catalyst life, catalyst activity, etc.

In preparing a catalyst of this invention, it will be appreciated thatthere is a very sensitive relationship between the temperature ofactivation and the time of caustic contact with starting alloy. Ingeneral, the higher the temperature, the longer should be the time forcaustic addition, because under such conditions localized overheating ofthe catalyst particles is apparently avoided or reduced to a minimumlevel. Localized overheating of alloy particles is theorized tointerfere with generation of a catalyst having the desiredcharacteristics associated with a Raney copper catalyst prepared asdescribed in the present invention and used in the hydrolysis reactionas described in the present invention, but thre is no intent to be boundby theory herein. If one employs a rapid reaction between alloyparticles and alkali metal hydroxide so that the hydrogen evolution rateis greater than that employed in the practice of this invention, thereis characteristically produced a lessening of catalyst activity. Whenthe caustic concentration exceeds about 20 weight percent of the liquidaqueous media, careful temperature control must typically be exercised.Most typically, the more concentrated the caustic solution, the lowershould be the reaction temperature and the shorter the contact time ofcaustic with alloy for maximizing catalyst activity.

As used herein, the term "gradual" includes not only variations inprocess conditions, but also incremental or intermittent addition ofalkali to alloy particles, or removal of a resulting aqueous medium fromthe zone of a given activation reaction. As can be determined from thepreceeding teachings, a reduction of the reaction rate of aluminum withcaustic is generating a catalyst for use in this invention is desired inorder to produce an active material. Such a reduction may be achieved,generally, by limiting the amount of caustic present, so that thecaustic is replaced in solution at a rate equal to the rate at which itis being consumed. In this way, a deviation between the alloy particletemperature and the caustic solution temperature will be minimized,resulting in an active catalyst, as desired.

Referring to FIGS. 1 through 4, as those skilled in the art willappreciate, there are seen four equipment configurations, each one ofwhich can be used to treat a group of starting alloy particles withaqueous caustic solution to produce an activated Raney copper catalystin accordance with the teachings of the present invention, provisionbeing made to vent hydrogen generated. Thus, in FIG. 1, these is seen anequipment configuration where a group of particles 9 are confined to areaction zone 10 and a caustic solution is added into the zone 10. Theliquid added into zone 10 through pipe 11 is allowed to accumulate inthe zone 10. At the end of the caustic addition, in accordance with thepreferred catalyst activation procedure of the present invention, andafter caustic addition is terminated, the resulting treated particles 9are removed from zone 10 as taught above. The particles 9 may be eitherinitially wet with water or substantially free from water before causticaddition is commenced. In one preferred mode, the particles 9 areimmersed in water.

In FIG. 2 is shown a system similar to FIG. 1; corresponding partsthereof are similarly numbered, but with the addition of prime marksthereto. The system of FIG. 2 is equipped with a drain arrangement 12which permits one to remove gradually from the vicinity of the group ofparticles 9' the medium which results after the caustic solution hasbeen brought into contact with the group of particles 9'. Preferably,the resulting aqueous medium is so removed at a volumetric rate which isabout equal to the rate of addition of the starting caustic solution.

In FIG. 3 is shown another system in which the parts similar to those ofFIG. 1 are similarly numbered, but with the addition of double primemarks thereto. Here, caustic solution is gradually added into reactionzone 10" through a conduit 13. After the caustic solution from conduit13 has contacted the group of particles 9", the resulting aqueous mediumis gradually removed through a conduit 14. In conduit 14 this resultingaqueous medium is conveyed to a connection region 15 where conduit 14 isinterconnected with a conduit 16. Fresh caustic solution is conveyedthrough conduit 16 and is mixed with the aqueous medium in conduit 14 inthe region of connection 15, so that a mixture of the aqueous medium andfresh caustic solution results, which mixture is then conveyed throughconduit 13 back into the reaction zone 10", as shown. Such a system asshown in FIG. 3 permits economical use of caustic, as those skilled inthe art will appreciate.

In FIG. 4 is shown another system in which the parts similar to those ofFIG. 1 are similarly numbered, but with the addition of triple primemarks thereto. Here caustic solution is gradually added into thereaction zone 10'" through a conduit 13'. After the caustic solutionfrom conduit 13' has contacted the group of particles 9'", the resultingaqueous medium is gradually removed through a conduit 14' in conduit 14,and the resulting aqueous medium is conveyed to a connection 17. Atconnection 17, a portion of the resulting medium is removed through aconduit 18. Effluent from conduit 18 may be discarded or otherwisedisposed safely if desired. The term "portion" here has reference to anyfraction of the resulting medium ranging from greater than 0 to lessthan about 100 weight percent or volume percent thereof. That portion ofthe resulting medium which is not removed from conduit 18 is conveyed byconduit 19 in connection region 15', where conduit 19' is connected witha conduit 16'. Fresh caustic solution is conveyed through conduit 16'and is mixed with the aqueous medium in conduit 19 in the region ofconnection 15', so that a mixture of the aqueous medium and freshcaustic solution results, which mixture is then conveyed through conduit13' back into the reaction zone 10'", as shown. Such a system as shownin FIG. 4 permits economical use of caustic and in addition permits oneselectively to remove spent caustic and accumulated aluminate salts fromthe system during catalyst activation, as those skilled in the art willappreciate.

In each of the systems of FIGS. 2, 3 and 4, the group of particles 9',9" or 9'", respectively, may be either initially wet with water, orsubstantially free from water, and, in one preferred mode, suchrespective groups of particles 9', 9" or 9'", are immersed in waterinitially. As those skilled in the art will appreciate, therepresentations in FIG. 1 through 4 are in no way to be considered aslimiting the actual conduit arrangement, method of caustic addition orresulting medium removal, equipment orientation, or the like. Thus, forexample, while, for simplicity, gravitational type systems are shown inFIGS. 1 through 4, a system based on horizontal flow, or vertical flow,can be employed, if desired, as can some combination of flow directionsof fluid over alloy particles during catalyst activation.

FIGS. 5, 6 and 7 illustrate for a particular catalyst of this inventionthe type of characteristic behavior associated therewith in a hydrolysisof acrylonitrile to acrylamide using such catalyst. Detailed descriptionof these individual plots appear in the examples below.

In a catalyst prepared as described herein, the aluminum content issomewhat variable. In general, it is not necessary to removesubstantially all of the aluminum present in the starting alloy, as hasheretofore been taught in the art for the preparation of Raney coppercatalysts (see the Kawaken reference). In general, a catalyst preparedin accordance with the present invention has at least two weight percentof aluminum contained therein. The exact form of this aluminum from achemical viewpoint is not known; it is possible that the aluminum is notin a pure form, but rather in the form of some compound or alloy withcopper or other element. The exact chemical nature of the aluminumpresent in a catalyst used in this invention is unknown presently.

It is a special feature of the present invention that relatively highquantities of aluminum can be present in a catalyst without interferingwith the desired relative activity in such a catalyst as herein taught.In general, it appears that one can produce a catalyst of this inventionhaving an aluminum content as much as 35% and still have a relativeactivity of at least about 2.0.

In general, when preparing a catalyst by the procedure as describedherein, it appears to be relatively easier to remove more aluminum fromsmall sized starting alloy particles than it is to remove equivalentamounts of aluminum from larger sized alloy particles and still achieverelative activities as desired and as taught herein. In one preferredmode of preparing a catalyst of this invention, one starts with alloyparticles which have sizes in the range of from about 0.02 to 0.5inches, and the amount of aluminum removed from such particles throughcontact with aqueous alkali metal hydroxide is preferably between about35% and 90% of the aluminum initially present in the starting alloyparticle, as conveniently determined through total hydrogen evolutionduring contacting or through the amount of soluble aluminum present inthe aqueous alkali metal hydroxide medium after completing thecontacting with the copper aluminum alloy particles. Hence, a preferredcatalyst for use in the process of this invention has an aluminumcontent of from about 9 to 40 weight percent (total catalyst weightbasis), and an activity of from about 2 to 3.5 measured as hereindescribed, and a particle size in the range of from about 0.02 to 0.5inches. As those skilled in the art will appreciate, a catalyst withinthe size range just given is particularly well adapted for use in anitrile hydrolysis process when one is employing a fixed bed catalystsystem as described herein.

EMBODIMENTS

The present invention is further illustrated by reference to thefollowing Examples. Those skilled in the art will appreciate that otherand further embodiments are obvious and within the spirit and scope ofthis invention from the teachings of these present Examples taken withthe accompanying specification.

EXAMPLE 1

Activation of alloy to Raney copper catalyst

A leaching reaction to activate a 50:50 copper aluminum alloy is carriedout using an apparatus arrangement as illustrated in FIG. 1. The alloy,which is in the form of particles ranging in size from about 0.09 to0.13 inch average diameter size, is placed in a wire basket which isrotated in a 1 to 3 liter reaction flask. The flask is provided with anitrogen purge inlet, a buret for caustic addition, a thermometer and ahydrogen outlet connected to a Wet Test Meter. Circulation of theleaching solution is accomplished by using a turbo-agitator.

After the alloy is placed in the basket mounted in the reactor flask, 6gms of deionized water per gram of alloy is added to the flask and theagitator is set for about 120 r.p.m. Heating to a reaction temperatureof 105° F. is undertaken concurrently with a 30 minute nitrogen purge.When the flask reaches 105° F. and the purge is completed, a 50 weightpercent sodium hydroxide solution is added continuously over a 380minute period to the system until 3 pounds of sodium hydroxide per poundof alloy have added, while controlling the temperature within ± 2° F.with external cooling.

The hydrogen evolution rate averages 0.0041 moles hydrogen per molealuminum initially in the alloy particles per minute during the sodiumhydroxide addition period. The hydrogen evolution rate subsequentlydecreases to a low level as conversion of aluminum approaches 80%.

After completing addition of sodium hydroxide, the reaction is continueduntil an estimated amount of about 80 to 90 weight percent of the totalaluminum present in the starting alloy has been leached. The reactionrate is monitored by measuring hydrogen evolution every 15 to 30minutes. Thereafter, the product catalyst is immediately removed fromthe leaching solution and placed into a large excess of deionized water.The product catalyst is rinsed with deionized water until the pH of therinse water approaches 7.0 after which the product catalyst is storedunder deionized water to prevent oxidation thereof.

EXAMPLE 2

Activation of alloy to Raney copper catalyst

A leaching reaction using an apparatus arrangement as illustrated inFIG. 2 to activate a 50:50 copper aluminum alloy is performed using asemi-batch fixed bed reactor constructed from three-fourth inch outsidediameter, 20 BWG tubing. The reactor is provided with a nitrogen purgeinlet, a buret for caustic addition, a thermometer, and a hydrogenoutlet connected to a Wet Test Meter.

At the bottom of the reactor a 3 to 4 inch bed of 4 mm glass beads areplaced on top of which is positioned a charge of starting alloy, whichis in the form of particles ranging from about 0.09 to 0.13 inch averagediameter. A second bed of similar bead thickness is placed on top of thealloy charge in the reactor. Thereafter, deionized water is circulatedthrough the bed while the reactor is being heated to 105° F.

Circulation of the leaching solution is accomplished by pumping a 1%caustic solution at a rate of 0.23 grams caustic per gram alloy per hourand allowing the resulting aqueous medium to be removed from the reactorat a rate approximately the pumping rate. The total quantity of causticcharged is 1.5 gms per gram of alloy. A liquid level, sufficient toimmerse the alloy and resulting catalyst, is maintained during theactivation with a liquid leg device so that greater heat transfercapabilities may be obtained.

The hydrogen evolution rate is 0.0039 moles hydrogen per mole aluminuminitially present in the alloy per hour. When the unit reaches 105° F.,the caustic solution is added until the total charge of about 3 grams ofcaustic per gram of alloy has been contacted with the alloy. Thereaction is continued until about 80 to 90 weight percent of the totalamount of aluminum estimated to be present in the starting alloy hasbeen leached, based on hydrogen evolution. The reaction rate isevaluated by monitoring the hydrogen evolution every 15 to 30 minutes.

The resulting product catalyst is then washed with deionized water untilthe pH of the wash water reaches the range of from about 7 to 7.5. Theproduct catalyst is then retained under water to prevent oxidation.

EXAMPLE 3

Activation of alloy to Raney copper catalyst

A leaching reaction using an apparatus arrangement as illustrated inFIG. 3 to activate a 50:50 copper aluminum alloy is performed using aone-half inch outside diameter semi-batch fixed bed reactor. The reactoris provided with a nitrogen purge inlet, a buret for caustic addition, athermometer, and a hydrogen outlet connected to a Wet Test Meter.Circulation of the leaching solution is accomplished by using a pumpthat is connected in a closed loop to the fixed bed reactor.

At the bottom of the reactor a 3 to 4 inch bed of 4 mm glass beads areplaced on top of which is positioned a charge of starting alloy, whichis in the form of particles ranging from about 0.09 to 0.13 inch averagediameter. A second bed of similar bead thickness is placed on top of thealloy charge in the reactor. Thereafter, a charge of 13.5 gms ofdeionized water per gram of alloy is recirculated through the bed whilethe reactor is being heated to 105° F. When the unit reaches 105° F., a50 weight percent sodium hydroxide solution is begun to be added at arate of about 0.23 of sodium hydroxide per gram of aluminum initiallypresent in the alloy per hour until a total charge of about 1.5 grams ofsodium hydroxide per gram of alloy have been added. The reaction iscontinued until about 80 to 90 weight percent of the total amount ofaluminum estimated to be present in the starting alloy has been leached,based on hydrogen evolution. The reaction rate is evaluated bymonitoring the hydrogen evolution every 15 to 30 minutes. The hydrogenevolution averages 0.0039 moles hydrogen per mole aluminum initially inalloy per minute during sodium hydroxide addition.

The resulting product catalyst is then washed with deionized water untilthe pH of the wash water reaches the range of from about 7 to 7.5. Theproduct catalyst is then retained under water to prevent oxidation.

EXAMPLE 4

Activation of alloy to Raney copper catalyst

A leaching reaction using an apparatus arrangement as illustrated inFIG. 4 to activate a 50:50 copper aluminum alloy is performed using asemi-batch fixed bed reactor constructed from three-fourth inch outsidediameter, 20 BWG tubing. The reactor is provided with a nitrogen purgeinlet, a buret for caustic addition, a thermometer, and a hydrogenoutlet connected to a Wet Test Meter. Circulation of the leachingsolution is accomplished by using a pump that is connected in a closedloop to the bed reactor.

At the bottom of the reactor a 3 to 4 inch bed of 4 mm glass beads areplaced on top of which is positioned a charge of starting alloy, whichis in the form of particles ranging from about 0.09 to 0.13 inch averagediameter. A second bed of similar bead thickness is placed on top of thealloy charge in the reactor. Thereafter, deionized water is circulatedthrough the bed while the reactor is being heated to 105° F. When theunit reaches 105° F., a 50 weight percent sodium hydroxide solution isbegun to be added at a range of 0.23 grams of sodium hydroxide per gramof alloy per hour until a total charge of about 2.3 grams of such sodiumhydroxide per gram of alloy have been added. During the sodium hydroxideaddition a portion of the resulting aqueous medium, approximately 25% ofthe total, is removed and the remaining 75% is recycled back to thereaction zone.

The reaction is continued until about 80 to 90 weight percent of thetotal amount of aluminum estimated to be present in the starting alloyhas been leached, based on hydrogen evolution.

EXAMPLE 5

Hydration Activity

A tubular reactor is formed from a 12 inch length of three-fourth inchstainless steel tubing with an internal diameter of 0.68 inches. Thereactor is vertically positioned in a bath of water and is equipped toallow introducing feed at the bottom and withdrawing product from thetop. The water bath is equipped with a heater and temperature controlledso the bath can be maintained at a preselected temperature.

When this reactor is used to determine the activity of a catalyst,during operation of this reactor, acrylonitrile and water are separatelypumped from volumetrically calibrated feed tanks, combined, heated, andintroduced into the bottom of the reactor. The reactor is maintainedunder pressure as necessary to allow maintaining liquid phaseconditions. Product leaving the reactor is cooled before reducingpressure to atmospheric. Product is collected in a final receiver.

Samples of product are analyzed for weight % acrylamide, weight %acrylonitrile, and weight % water to determine conversion levels (100weight percent total product weight basis).

The procedure to determine catalyst activity is as follows: A measured150 gms of catalyst (on a dry weight basis) is charged to the tubularreactor so as to occupy approximately 90 cubic centimeters and a seriesof tests are run as previously described. The tests are run at differentcontact times with all other variables held constant as follows:

1. Arithmetic mean catalyst bed temperature of 175° F.

2. feed composition 100 weight % basis of 25 weight % acrylonitrile and75 weight % water.

Contact time is inversely measured as weight hourly space velocity(WHSV), which is defined as weight hourly feed rate divided by catalystweight in the reaction zone.

The contact times are varied to bracket a 35% conversion level. The WHSVrequired for 35% conversion (WHSV₃₅) is estimated by graphical orstatistical interpolation. The catalyst activity (a) is then calculatedfrom the following expression:

a = 1.07 (WHSV₃₅)

The ranges for catalyst activity are elsewhere herein indicated. Allcatalyst activity valves in this application are measured by theprocedure described in this Example.

WHSV's in the range of 0.8 to 10.0 are useful starting points to bracketthe space velocity required for 35% conversion (WHSV₃₅), the last beingan abbreviation for weight hourly space velocity needed for 35%conversion.

For testing the activity of very small particles of catalyst in therange, say, from about 0.1 to 0.002 inch, one should use short runs andrelatively short catalyst beds to avoid or to minimize pressure dropsthrough the test bed.

                                      TABLE I                                     __________________________________________________________________________                                                Hydrogen Ero-                     Catalyst Activation Conditions              lution rate (moles                          NaOH   Weight Ratio                                                                         NaOH    Total       H.sub.2 per mole                                                                       % aluminum                  Temperature                                                                          Concentration                                                                        of total NaOH                                                                        addition (2)                                                                          reaction                                                                           Contacting                                                                           initially in                                                                           in                                                                                  Acti-yst           Case                                                                             (° F)                                                                         % (1)  to alloy                                                                             time(minutes)                                                                         time(hrs)                                                                          method per min.)                                                                              (3)   vity               __________________________________________________________________________    1  85     20     1.2    --      4    alloy par-                                                                           --       31    1.0                2  85     20     1.1    --      4  1/2                                                                             ticles are                                                                           --       --    1.38               3  85     20     1.3    --      5  1/2                                                                             added to                                                                             --       66    1.0                                                     both of 20%                                                                   NaOH aque-                                                                    ous solution                             4  85     20     1.5    49      1  1/3                                                                             method of                                                                            0.009    36    2.0                5  85     20     1.5    90      7  1/2                                                                             example 1                                                                            0.0068   12    3.15               6  68     20     1.5    35      7           0.0043   24    3.0                7  150    20     1.1    45      3           0.0225    3    1.76               8  110    20     1.5    215     10   method of                                                                            0.005    12    2.8                                                     example 2                                __________________________________________________________________________     Notes:                                                                        (1) NaOH concentration is calculated as the ratio of the weight of total      NaOH (on a 100% NaOH basis) charged to the weight of initial charge of        water plus the weight of 50% NaOH solution added times 100.                   (2) The NaOH is added as a 50% solution at a substantially uniform rate       over the indicated time period.                                                (3) Aluminum contents of the catalysts are indirectly estimated from         total hydrogen evolved.                                                  

Table 1 summarizes the catalyst activation conditions used in preparingeight different catalysts and the catalyst activities which aredetermined by testing in the described manner. These examplesdemonstrate that catalysts activated by incrementally adding sodiumhydroxide to a catalyst activation system have much higher activitiesthan catalysts activated by adding alloy granules to a bath of aqueoussodium hydroxide solution, as determined by Cases 1, 2, and 3 versusCases 4, 5, 6 7, and 8. These examples also demonstrate that conductingthe reaction under mild conditions and low hydrogen evolution rates willresult in catalysts of higher activity, as demonstrated by Case 7 versusCases 4, 5, 6 and 8.

EXAMPLE 6

Hydrolysis process for testing catalyst life

A system for hydrolyzing acrylonitrile to acrylamide is a reactor in thedesign of a double pipe heat exchanger with a flow system as indicatedin FIG. 2. The inner tube which constitutes the reaction zone which hasa 5 foot length and is formed of 316 stainless steel and has a 1 inchoutside diameter schedule 105 pipe. The inner tube is uniformlysurrounded by a jacket which is provided with an inlet at the bottom ofthe jacket and also with an outlet at the top of the jacket to allowcirculation of a heat transfer medium to remove heat generated from thereaction. A temperature sensing device is installed in the inner pipe toallow temperature measurements throughout the reaction zone.

During operation of the reactor, acrylonitrile and water are separatelypumped from volumetrically calibrated feed tanks, combined, heated, andintroduced into the bottom of the reactor. The reactor is maintainedunder pressure to allow maintaining liquid phase conditions. In thisExample, the following process conditions apply to the operation in testof a catalyst prepared in the manner of Example 6;

    ______________________________________                                        Reactor temperature                                                                            220° ± 2° F                                 Weight percent acrylonitrile                                                                   35 ± 1%                                                   in the feed                                                                   Weight hourly space velocity                                                                   1.5 ± 0.3                                                                              pounds of                                                                     feed per pound                                                                of catalyst per                                                               hour.                                            ______________________________________                                    

As previously mentioned, the catalyst here used in a nominal 50% copper,50% aluminum alloy activated in the manner described in this invention.A quantitative analysis of this catalyst after activation indicates thatthe activated catalyst composition is 81 weight percent copper and 19weight percent aluminum. The catalyst, which is in the form of particlesranging in size from about 0.06 to 0.125 inches in diameter, is typicalof other catalysts prepared as taught herein and evaluated in theprocess of this invention.

Product leaving the reactor is cooled before being reduced toatmospheric pressure. Such product is collected in a final receiver andanalyzed for acrylamide, acrylonitrile and water content. Based on theserespective analyses, conversion level of acrylamide, and activity of thecatalyst at a particular point in time, are each determined.

The following Table 2 shows conversion level to acrylamide as a functionof time of continuous operation using the process system described inthis Example. This Table indicates the low activity loss of a catalystprepared as described in this invention and used in the process of thisinvention over a period of 541 continuous operating hours with aproduction of 243 pounds of acrylamide per pound of catalyst. The highconversion level that is obtainable after this 541 hours of operationwith this catalyst indicates the unexpected and surprising superiorityof this catalyst over other Raney copper catalysts found in prior artand used in this hydrolysis reaction.

                  TABLE 2                                                         ______________________________________                                        Test     Elapsed Operating Time*                                                                          % Conversion                                      ______________________________________                                        3        55                 72.9                                              4        82                 68.9                                              5        154                65.0                                              6        178                63.2                                              7        199                60.8                                              8        256                62.8                                              9        279                63.4                                              10       331                53.8                                              11       353                54.4                                              12       401                56.2                                              13       422                57.0                                              14       455                59.2                                              15       467                60.7                                              16       491                57.6                                              17       541                54.8                                              ______________________________________                                         *Hours                                                                   

EXAMPLE 7

Reaction Rate Information

Using a method similar to the method of catalyst activation as describedin Example 1, reaction rate information of this catalyst system isobtained. This information describes some of the kinetic rateinformation necessary to understand the reaction of a copper-aluminumalloy, as herein described, with caustic.

The reaction rate dependency on temperature is illustrated in FIG. 5where an Arrhenius-Plot is shown. The ordinate is in units or reciprocalminutes, and is the reaction rate coefficient, K, wherein the values ofK have been multiplied by 104. The abscissa is in the units ofreciprocal degrees Kelvin and the value of the points on the abscissahave been multiplied by 10³.

The effect of catalyst particle size is found to be linear over aparticle diameter range of from about 0.04 to 2.0 inches, as illustratedby the data of FIG. 6. The ordinate in this figure is in units ofreciprocal minutes, and is the reaction rate coefficient, K, wherein thevalues of K have been multiplied by 10³. The abscissa is in units ofinches diameter and reflects the average particle size diameter.

Variations in the caustic concentration can result in non-uniformchanges in the reaction rate but such changes occur in an expectedpattern, i.e., higher caustic concentrations yield a faster reactionrate and systems with the same caustic concentration react faster if thetemperature or the NaOH to aluminum mole ratio is increased, asillustrated in FIG. 7. The ordinate is in units of reciprocal minutes,and is the reaction rate coefficient K, wherein the values of K havebeen multiplied by 10³. The abscissa is in the units of weight percentsodium hydroxide and represents the concentration of sodium hydroxidepresent in the activating solution.

This information is useful in preselecting catalyst activationconditions which result in desirably low reaction rates that will resultin catalysts of high activity.

We claim:
 1. In a process for making a Raney copper catalyst whichcontains from about 2 to 45% by weight on a 100 weight percent totalcatalyst weight basis of aluminum, said catalyst having a relativeactivity of at least about 2.0 and having been prepared by contacting anaqueous medium containing dissolved therein alkali metal solution to agroup of copper/aluminum alloy particles, the improvement whichcomprises conducting such contacting by incrementally adding aqueousdissolved alkali metal hydroxide to said medium during said contactingover said time interval,A. said aqueous alkali metal hydroxide solutioncontaining from 0.5 to 40 weight percent dissolved alkali; B. said grouphaving an average particle size diameter in the range from about 0.002to 0.5 inch; C. said copper/aluminum alloy having initially a copper toaluminum weight ratio of from about 30:70 to 70:30; D. said contactingbeing accomplished over a total time interval of from about 2 to 30hours; E. the addition rate of such alkali metal hydroxide contactingbeing from about 0.01 to 7 moles of alkali metal hydroxide per mole ofaluminum initially present in said alloy particles per hour; F. thetotal quantity of alkali metal hydroxide so added being in the range offrom about 0.5 to 20 moles of alkali metal hydroxide per mole ofaluminum initially present in said alloy particles; and G. the resultingaqueous medium produced in such contacting being maintained at atemperature in the range from about 32 to 180° F.
 2. In an improvedprocess for making a Raney copper catalyst, by contacting a prechosengroup of copper aluminum alloy particles confined to a reaction zonewith a liquid aqueous medium containing dissolved therein alkali metalhydroxide, the improvement which comprises maintaining during suchcontacting a reaction rate between said particles and of said hydroxidesuch that not more than about 0.02 moles of hydrogen per mole of saidaluminum initially present in said alloy on a 100 weight percent initialalloy basis is evolved per minute, such contacting being conducted whilekeeping a bulk temperature in said medium in the region of said groupranging from about 0 to 82° C, such contacting being continued until atleast about 35 weight percent of said aluminum initially present in saidalloy on a 100 weight percent total initial alloy basis is removed, saidalloy particles initially having a ratio of copper to aluminum in therange from about 30:70 to 70:30, said alloy particles further initiallyhaving average particle diameters in the range of from about 0.002 to0.5 inch, the total molar quantity of alkali metal hydroxide charged tosaid medium during the total time of such contacting being at leastabout 0.5 times the number of moles of aluminum initially present insaid alloy particles, the total weight of water initially present insaid medium at the beginning of such contacting plus water added to saidmedium during such contacting ranges from about 1.5 to 100 times thetotal weight quantity of dissolved alkali metal hydroxide so contactedwith such particles.
 3. The process of claim 2, wherein, during saidcontacting,A. said alkali metal hydroxide is added to said mediumincrementally at a rate which ranges from about 0.01 and 7.0 moles ofalkali metal hydroxide per mole of aluminum initially present in saidparticles per hour, B. the total quantity of alkali metal hydroxidebeing added to said medium ranges from about 0.5 to 20 moles of alkalimetal hydroxide per mole of aluminum initially present in said group,and C. said addition of alkali metal hydroxide to said medium isconducted in a total time interval which ranges from about 2 to 200hours.
 4. The process of claim 2 wherein said particles are initiallyimmersed in water before said contacting.
 5. The process of claim 2wherein said medium initially contains at least about 1.0 weight percentdissolved alkali metal hydroxide and said medium is maintainedthroughout said contacting at a temperature not above about 180° F. 6.The process of claim 5 wherein substantially all of said alkali metalhydroxide is initially present in said medium and said medium isinitially bulk added to a reaction zone wherein said alloy particles arecontained, and said bulk zone temperature is maintained below about 70°F during said contacting until a least about 35 weight percent of thealuminum initially present in said alloy particles is removed.
 7. Theprocess of claim 3 wherein, after said alkali metal hydroxide has beenso added to said medium, said contacting is continued the total time ofcontacting being for a period of time of not more than about 200 hours.8. The process of claim 2 wherein during said contacting said alloyparticles have average particle diameters ranging from about 0.02 to 0.5inches, and said contacting is achieved by maintaining said particles ina substantially fixed spatial position and said medium is continuouslycirculated past said particles while said particles are so maintained.9. The process of claim 8 wherein during said contactingA. said alkalimetal hydroxide is added to said medium incrementally at a rate whichranges from about 0.01 and 7.0 moles of alkali metal hydroxide per moleof aluminum initially present in said particles per hour, B. the totalquantity of alkali metal hydroxide being added to said medium rangesfrom about 0.5 and 20 moles of alkali metal hydroxide per mole ofaluminum initially present in said group, and C. said addition of alkalimetal hydroxide to said medium is conducted in a total time intervalwhich ranges from about 2 to 200 hours.
 10. The process of claim 2wherein during said contacting said alloy particles have averageparticle diameters ranging from about 0.002 to 0.01 inch, and saidparticles and said medium are agitated to an extent sufficient tosuspend said particles in said medium during said contacting.